“For many years, oncologists have known that cancers can secrete complex molecules into the blood and that levels of these molecules can be easily measured. These so-called ‘tumor markers’ are traditionally associated with a single dominant cancer type, for example Prostate Specific Antigen (PSA) linked to prostate cancer, Carcinoembryonic antigen (CEA) to colorectal cancer, CA125 to ovarian cancer, CA19.9 to pancreatic cancer and CA27.29 to breast cancer. However, the real challenge has been to determine a practical use for these markers. They don’t appear to be useful as a means of screening otherwise healthy people for evidence of underlying cancers.”